The scale on a map is 8cm : 10km. If two cities are 40cm apart on the map, what is the actual distance in km between the two cities?
Answer: The scale means that every 8cm on the map corresponds to an actual distance of 10km. A distance of 40cm on the map is the same as 5 $\cdot$ 8cm. The actual distance between the two cities is 5 $\cdot$ 10km, or 50km.